1. Field of the Invention
The present invention relates to a piezoelectric actuator in the form of a plate used in a piezoelectric ink jet printer head, and more specifically to configuration of common electrodes and individual electrodes of such a piezoelectric actuator.
2. Description of Related Art
FIG. 1 shows a conventional piezoelectric ink jet printer head 100 disclosed in U.S. Pat. No. 5,402,159. As shown in FIG. 1, the conventional head 100 includes a nozzle plate 117, a cavity plate 115, a piezoelectric actuator 111 in the form of a plate, and a back plate 119. The nozzle plate 117 is formed with a plurality of nozzles 118. The cavity plate 115 is formed with a plurality of ink cavities 116, each corresponding to one of the plurality of nozzles 118.
The piezoelectric actuator 111 includes a plurality of piezoelectric ceramic layers 110 called green sheets. Individual electrodes 112 are formed on each of a half of the piezoelectric ceramic layers 110, and a common electrode 113 is formed on each of another half of the piezoelectric ceramic layers 110. These two types of layers are alternatively arranged one on the other to have a laminated structure. Each of the individual electrodes 112 corresponds to one of the ink cavities 116. The common electrodes 113 are common to all the ink cavities 116.
The piezoelectric actuator 111 also includes outer electrodes 114 formed on its side surface by vacuum metallizing, metal spattering, conductive paste coating, or the like. Each outer electrode 114 electrically connects one of the sets of the individual electrodes 112 to the outside.
However, in this configuration, when the end portion of each individual electrode 112 may not reach the side surface of the piezoelectric actuator 111, the electrical connection between the individual electrode 112 and the outer electrode 114 would be insufficient. Also, during the conductive paste coating and the like for forming the outer electrode 114, the orientation of the piezoelectric actuator 111 is changed such that its side surface faces upward. This complicates the production process.
Moreover, there is a danger that the electrical connection of the electrodes 112 and 114 is damaged by accidentally contacting a handler or a tool during the production or assembly of the piezoelectric actuator 111.
In order to overcome these problems, as shown in FIGS. 2 through 4, Japanese Patent Publication No. HEI-7-96301 has proposed to form a lead-out electrode 8a, 9a to each of the individual and common electrodes 8, 9. A plurality of first through-holes 2 are formed to penetrate through piezoelectric ceramic sheets 6 and the lead-out electrodes 8a of the corresponding individual electrodes 8. Also, a second through hole 3 is formed to penetrate through piezoelectric ceramic sheets 6 and the lead-out electrodes 9a of the common electrodes 9. Then, each of the first and second through holes 2, 3 are filled with conductive paste, so that the individual electrodes 8 and the common electrodes 9 are electrically connected to an external electrode through the through holes 2 and 3.
In this case, the through holes 2, 3 are formed to all the piezoelectric ceramic sheets 6, but not to a cavity plate 4, which is formed with ink cavities 4a and an ink channel 4b. However, because the cavity plate 4 is formed from a piezoelectric ceramic sheet also, when the through holes 2, 3 are formed connected to the ink cavities 4a or the ink channel 4b, short circuits will result. Therefore, in order to avoid the short circuit, positions of the through holes 2, 3 need to be carefully selected, and so the configuration of a piezoelectric actuator is strictly restricted.
Accordingly, it is an objective of the present invention to overcome the above problems, and also to provide a piezoelectric actuator with a configuration enabling simplifying a production process while avoiding short circuits and warping.
In order to achieve the above and other objectives, there is provided an ink jet print head including a cavity plate and a piezoelectric actuator. The cavity plate is formed with a plurality of nozzles and a plurality of pressure chambers each corresponding to one of the plurality of nozzles. The piezoelectric actuator includes a plurality of first piezoelectric sheets extending in a first direction, a plurality of second piezoelectric sheets extending in the first direction, a plurality of individual electrodes each corresponding to one of the plurality of pressure chambers and formed on the surface of the first piezoelectric sheets, and a plurality of common electrodes common to the plurality of pressure chambers and formed on the surface of the second piezoelectric sheets. The first piezoelectric sheets and the second piezoelectric sheets are arranged one on the other in alternation in a second direction perpendicular to the first direction so as to form a laminated structure. One of the first and second piezoelectric sheets at an end of the laminated structure lies on the cavity plate. The piezoelectric actuator is formed with first through holes formed in each of the first and second piezoelectric sheets in the second direction, except the one of the first and second piezoelectric sheets lying on the cavity plate. Each of the plurality of individual electrodes is formed at a position corresponding to the first through holes on the first piezoelectric sheets. The first through holes is filled with conductive material, thereby electrically connecting corresponding ones of the plurality of individual electrodes.
There is also provided a piezoelectric actuator used in a recording head including a cavity plate formed with a plurality of nozzles aligned in a first direction, and a plurality of channels each corresponding to one of the plurality of nozzles. The piezoelectric actuator includes a plurality of first piezoelectric sheets having a surface, a plurality of second piezoelectric sheets having a surface, and a plurality of first electrode patterns. The plurality of first piezoelectric sheets and the plurality of second piezoelectric sheets are arranged one on the other in a thickness direction perpendicular to the first direction. Each of the first electrode patterns is formed on the surface of one of the plurality of first piezoelectric sheets, and formed with a gap having a width in a second direction perpendicular to both the first direction and the thickness direction. The gaps of ones of the first electrode patterns are positioned shifted in the second direction from the gaps of another ones of the first electrode patterns.